The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. The main pole of a magnetic head is used to deliver flux to a recording medium, thereby flipping the magnetic orientation of bits within the recording medium. The stronger the flux is, the easier it is to flip the bit, thereby allowing data to be recorded to the recording medium more easily.
However, when the main pole is not shielded effectively, the flux may be delivered to bits in a track adjacent to the track on which the bit is being recorded causing these bits in the adjacent track to unintentionally flip, referred to as adjacent track interference (ATI). Also, the flux may be delivered to bits in a track located some distance from the track on which the bit is being recorded and may cause these bits to unintentionally flip, referred to as far track interference (FTI).